Controlling HIV/AIDS in Ireland: The Implications for Health Policy of Some Epidemic Forecasts

This paper is set within the context of growing opiate use, and in it we develop and apply a modelling framework that is designed to forecast HIV prevalences and AIDS incidences that are consistent with various control scenarios related to the medium-term behaviour of the epidemic in Ireland. This task involves, first, fitting a process-based HIV model to AIDS incidence series for both Ireland and the United Kingdom to estimate national variations in the force of infection between the major risk populations. Second, these results are used to calibrate extended models which employ time-dependent parameters to imitate the effects of changed behaviours and other preventative actions. Third, the impacts of such interventions on the size and duration of the epidemic are illustrated by altering the values of the epidemiological or behavioural parameters at some time during the simulation interval. These results are then presented as control charts which record both the magnitude of the preventative action (such as a reduction in the number of sexual or needle-sharing partners) and the timing of its implementation. Last, in the discussion the implications of these findings for the development of health policy for HIV/AIDS in Ireland are considered. In particular, a comparison of the control charts suggests that, if it has not already taken place, the need for stringent interventions amongst intravenous drug users would appear to be imminent, whereas the position for gay men is less critical.